1. Field of the Invention
This invention relates to electrical ballasts used to start and energize fluorescent lamps.
2. Background
Industry has produced a large number of different ballast circuits and controllers for operating fluorescent lamps. A relative few enjoy commercial success and are widely used. This is primarily due to the ballast's cost of manufacture and secondarily, to their suitability to lamp installation needs.
Fluorescent lamps come in different size power ratings and in two groups of linear and compact lamps. Linear lamps are the familiar long lamps commonly used in industrial lighting suspended from the ceiling and in all manner of retail establishments. Compact lamps are of various shapes and may be used for table lamps or other locations demanding a small size lamp. Each type and rating lamp requires a ballast to match it for starting and operation. However, one or more matched ballasts may be used for several lamps connected in series or parallel, providing that the lamps are the same type and rating. As a consequence, lamp producers and retailers have to stock a large variety of ballast ratings and types in order to meet demand.
Presently available ballasts for fluorescent lamps have at least two undesirable operating characteristics. These are the output of a square wave voltage to a lamp, and a possible variation in lamp current, including spikes. The square wave voltage includes harmonics that in time, can severely stress and degrade the performance of the lamp. Variations in lamp current can similarly stress the lamp, leading to early failure. The ballast may also fail. Several ballasts and controllers exist that purport to counter or alleviate these characteristics. However, these devices are expensive to manufacture and generally do not find favor with the consumer because of their cost.
There is therefore a need for a single ballast that may be used to start and operate a range of different rated fluorescent lamps, greatly reducing the number of required ballast ratings in manufacture and storage. There is also a need for a single ballast that can operate different types and ratings of fluorescent lamps in any desired connection configuration. An ongoing need is improving the output characteristics of the ballasts to reduce stress on the lamps without increasing ballast cost.